Residence time distribution method and apparatus for operating a curvilinear pressure vessel where transport phenomena take place

Abstract

A method and apparatus for operating a pressure vessel containing a bed of particulate material comprising substantially leveling the bed and employing a fluid flow distributor above the bed.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] This invention relates to the operation of a pressure vessel and apparatus for carrying out such operation. [0003] 2. Description of the Prior Art [0004] Although, for sake of clarity and brevity, this invention will be described in respect of the solution polymerization of ethylene, it is to be understood that this invention applies generally to curvilinear pressure vessels that operate at an elevated pressure, e.g., at least about 1,000 psig, and that contain a bed of particulate material through which a process fluid is to flow in a substantially uniform manner. For example, this invention can be applied to adsorbent beds, catalyst beds, and fixed beds such as those used in processes such as polymer formation. [0005] Heretofore, linear high density polyethylene (HDPE) has been formed by polymerizing ethylene while dissolved in a solvent such as hexane. The resulting solvent solution also contains a polymerization...

AI Technical Summary

Benefits of technology

[0014] Pursuant to this invention, plug flow of a process fluid through a bed in a pressure vessel is more closely approached by the combination of substantially flattening the upper surface of the bed, and employing a flow distributor in the vicinity where the process fluid enters the vessel.

Problems solved by technology

The curvilinear shape of a high pressure adsorber, the conical shape of the adsorbent bed in the adsorber, and the right angle turn the single phase solution must make after it enters the nozzle of the adsorber, all work against achieving anything like plug flow of the solution through the adsorbent bed.

This causes mal-distribution of solution as it passes to and through the bed, which results in channeling of solution through localized portions of the bed.

This channeling causes underutilization of the adsorbent throughout substantial volumes of that bed, while other portions, where the channeling occurs, are forced to treat too much solution.

If two-phasing is allowed to continue unchecked, the vessels in which it is occurring will eventually plug up with solid polyethylene thereby requiring shut down of the plant, and clean up of at least the affected vessels, a costly event in terms of lost production and clean-up costs.

Mal-distribution of single phase solution flow through an adsorber bed can cause two-phasing and polymer deposition in the bed due to an undesired change in pressure where the solution channels through the bed.

This can lead to plugging of at least sections of the bed, up to, and including, the entire bed if left unchecked.

This then necessitates a premature and costly shut down of the adsorber and replacement of the bed with fresh adsorbent.

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